Motion picture encoding device and motion picture decoding device

ABSTRACT

When a prediction is made between fields with different parity, the predicative efficiency of a chrominance vector is improved by adaptively switching the generation of a chrominance motion vector depending on encoding/decoding field parity (top/bottom) and a reference field parity (top/bottom), and the coding efficiency is improved accordingly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motion picture encoding device and amotion picture decoding device, which have an inter-field predictionmode.

2. Description of the Related Art

Generally, motion picture data is large in size. Therefore, when motionpicture data is transmitted from a transmitting device to a receivingdevice or when it is stored in a storage device, highly efficientencoding is applied to motion picture data. In this case, “highlyefficient encoding” is an encoding process of converting a specific datastring into another data string, and compressing the amount of data.

There are two types of motion picture data: one is mainly composed ofonly frames and the other is composed of fields. A prior art forcompressing a field image is mainly described below.

As the highly efficient encoding method of motion picture data, aframe/field prediction encoding is known.

FIG. 1 shows a block diagram of the configuration of the frame/fieldpredictive encoding device.

This encoding method utilizes the fact that a plurality of segments ofmotion picture data has high correlation in a time direction with eachother. The operation shown in FIG. 1 is roughly described below. Asubtracter 39 generates a differential image between an inputtedoriginal image and a predicted image, and an orthogonal transform unit31, a quantization unit 32 and a coefficient entropy encoding unit 40encode the differential image. An inverse quantization unit 33 and aninverse orthogonal transform unit 34 reproduce the differential imagefrom the output of the quantization unit 32. Then, a decoded imagegeneration unit 35 decodes the encoded image using the reproduceddifferential image reproduced by the decoded image generation unit 35and the predicted image used at the time of encoding. A decoded imagestorage unit 36 stores the reproduced image. Then, motion vectorcalculation unit 37 calculates a motion vector between the reproducedimage and a subsequent input image, and a predicted image generationunit 38 generates a predicted image using the motion vector. Thegenerated motion vector is encoded by a vector entropy encoding unit 41and is outputted through a MUX 42 together with the encoded coefficientdata encoded by the coefficient entropy encoding unit 40. In otherwords, since in motion picture data, there is generally high similaritybetween frame/field data at a specific time and frame/field data at asubsequent time, the inter-frame/field predictive encoding methodutilizes such a property. For example, in a data transmission systemadopting the inter-frame/field predictive encoding method, atransmitting device generates motion vector data indicating displacementfrom previous frame/field image to a target frame/field image, anddifferential data between a predicted image in the target frame/fieldwhich is generated from the previous frame/field image using its motionvector data and a real image in the target frame/field, and transmitsthe motion vector data and the differential data to a receiving device.The receiving device reproduces the image in the target frame/field fromthe received motion vector data and differential data.

So far, the summary of the frame/field predictive encoding has beendescribed with reference to FIG. 1. Next, frame predictive encoding andfield predictive encoding are described below.

FIGS. 2 and 3 show a format used to encode a field image that iscommonly used in ISO/IEC MPEG-2/MPEG-4 (hereinafter called “MPEG-2” and“MPEG-4”, respectively) and the final committee draft of ITU-TH.264/ISO/IEC MPEG-4 Part 10 (Advanced video coding (AVC)) (“Joint FinalCommittee Draft (JFCD) of JointVideo Specification (ITU-T REC,H.2641ISO/IEC 14496-10 AVC)”, JVT-D157, or ISO/IEC JTC1/SO29/WG11MPEG02/N492, July 2002, Klagenfurt, AT) (hereinafter called “AVC FCD”),which ITU-T and ISO/IEC jointly were standardizing as of August 2002.Specifically, each frame is composed of two fields: a top field and abottom field. FIG. 2 shows the respective positions of a luminancepixels and a chrominance pixels, and a field to which each pixelbelongs. As shown in FIG. 2, odd number-ordered luminance lines, such asa first luminance line (50 a), a third luminance line (50 b), a fifthluminance line (50 c), a seventh luminance line (50 d), etc., belong tothe top field, and even number-ordered lines, such as a second luminanceline (51 a), a fourth luminance line (51 b), a sixth luminance line (51c), a eighth luminance line (51 d), etc., belong to the bottom field.Similarly, odd number-ordered chrominance lines, such as a firstchrominance line (52 a), a third chrominance line (52 b), etc., belongto the top field, and even number-ordered chrominance line, such as asecond chrominance (53 a), a fourth chrominance line, etc., belong tothe bottom field.

Each of the top and bottom fields indicates an image at a differenttime. Next, the time/spatial disposition of the top and bottom fields isdescribed with reference to FIG. 3.

In FIG. 3 and after, the technology of the present invention relates tothe vertical component of a motion vector. Therefore, in thisspecification, horizontal pixel components are not shown, and all thehorizontal components of the motion vector are assumed to be 0 forconvenience sake. However, in order to show conventional problems andthe effects of the present invention, the positional relation betweenluminance and chrominance in each field is accurately shown.

In FIG. 3, the vertical and horizontal axes represent the pixel positionof a vertical component in each field and the elapse of time,respectively. Since there is no positional change in a field of thehorizontal component of each image, in FIG. 3, its horizontal pixelcomponent is not shown nor is described.

As shown in FIG. 3, the pixel position of a chrominance componentdeviates from the pixel position in a field of a luminance component bya quarter vertical pixel. This is because relationship of pixelpositions as shown in FIG. 2 is achieved when a frame is constructedfrom both Top and Bottom fields. If it is based on a NTSC format, eachtime interval between adjacent top and bottom fields (64 a: 65 a, 65 a:64 b, etc.) is approximately 1/60 seconds. Each time interval betweentwo consecutive top fields (64 a: 64 b, etc.) or between two consecutivebottom field (65 a: 65 b, etc.) are approximately 1/30 seconds.

Next, the frame predictive encoding mode of a field image and its fieldprediction, which is adopted in MPEG-2 and AVC FCD, are described.

FIG. 4 shows a method for constructing a frame using two consecutivefields (adjacent top and bottom fields) in a frame predictive mode.

As shown in FIG. 4, a frame is reconstructed by two time-consecutivefields (top and bottom fields).

FIG. 5 shows a frame predictive mode.

In FIG. 5 it is assumed that each frame, such as 84 a, 84 b, 84 c, etc.,is already reconstructed by two consecutive fields (top and bottomfields), as shown in FIG. 4. In this frame predictive mode, a frame tobe encoded which is composed of top and bottom fields is encoded. As areference image, one reference frame is constructed by two consecutivefields (top and bottom fields) stored for reference use, and is used topredict the target frame to be encoded. Then, these two frame images areencoded according to the process flow shown in FIG. 1. In the expressionmethod of a motion vector of this frame predictive encoding mode, a zerovector, that is, (0,0) indicates a pixel located in the same spatialposition. Specifically, the motion vector (0, 0) of a luminance pixel 82that belongs to frame #2 (84 b) indicates the pixel position 81 of frame#1 (84 a).

Next, a field predictive encoding mode is described.

FIG. 6 shows a predictive method in an inter-field predictive mode.

In a field predictive mode, an encoding target is one top field (94 a,94 b, etc.) or bottom field (95 a, 95 b, etc.) that is inputted as anoriginal image. As a reference image, a top field or bottom field thatis stored before can be used. In this case, it is generally defined thatthe fact that an original image field parity and a reference fieldparity are the same means that the original image field and thereference field both are top fields or bottom fields. For example, in aprediction 90 between fields with the same parity shown in FIG. 6, anoriginal image field (94 b) and a reference field (94 a) both are topfields. Similarly, it is generally defined that the fact that anoriginal image field parity and a reference field parity are differentmeans that one of original image and reference fields is a top field andthe other is a bottom field. For example, in a prediction 91 betweendifferent parity fields shown in FIG. 6, the original image field is abottom field (95 a) and the reference field is a top field (94 a). Then,these original image and reference fields are encoded according to theprocess flow shown in FIG. 1.

In the prior art, in both frame and field modes, a motion vector iscalculated based on a pixel position in each frame/field. Here, aconventional motion vector calculation method and a conventional pixelcorresponding method used when a motion vector is given are described.

FIG. 7 defines the coordinates of a frame/field image widely used inMPEG-2 coding, MPEG-1 coding, AVC FCD coding, etc. White circles in FIG.7 are pixel definition positions in target frames/fields. In thecoordinates of this frame/field image, the upper left corner isdesignated as the origin (0,0), and values 1, 2, 3, etc., aresequentially assigned to both horizontal and vertical pixel definitionpositions. Specifically, the coordinates of a pixel that are located atthe n-th horizontal position and the m-th vertical position are (n,m).Similarly, the coordinates of a position interpolated among the pixelsare also defined. Specifically, since a position 180 marked with a blackcircle in FIG. 7 is located at 1.5 pixels in the horizontal directionfrom the pixel located in the upper left corner and at 2 pixels in thevertical direction, the coordinates of the position 180 is expressed as(1.5, 2). In a field image, there are only a half of the pixels of aframe image in the vertical direction. However, even in this case, thecoordinates of a pixel are defined in the same way as in FIG. 7, basedon pixel positions located in each field.

Next, the definition of a motion vector between fields is describedusing the coordinate system shown in FIG. 7.

FIG. 8 shows a conventional calculation method of a motion vectorbetween corresponding pixels between fields. The definition of a motionvector requires the position of a coding field and the position of areference field. A motion vector is defined between these two points.Thus, a motion vector between a coding field coordinates 201(X_(s),Y_(s)) and a reference field coordinates 202 (X_(d), Y_(d)) iscalculated. In the conventional calculation method of a motion vectorbetween pixels corresponding to between-fields, a motion vector iscalculated by the same method described below, regardless of whether thecoding field or reference field is a top field or a bottom field.Specifically, coding field coordinates 201 (X_(s), Y_(s)) and referencefield coordinates 202 (X_(d), Y_(d)) are inputted to a motion vectorcalculation unit 200, and as a motion vector 203 between these twopoints, (X_(d)−X_(s), Y_(d)−Y_(s)) is given.

FIG. 9 shows a conventional method for calculating a pixel that ispointed by a motion vector defined between fields. In this case, it isassumed that a motion vector is calculated by the method shown in FIG.8. The calculation of reference frame/field coordinates requires acoding frame/field position and a motion vector. In the case shown inFIG. 9, it is assumed that a motion vector 211(X,Y) is given for codingfield coordinates 212 (X_(s), Y_(s)), and reference field coordinatescan be calculated using both the motion vector 212(X,Y) and the codingfield coordinates 212 (X_(s), Y_(s)). In the conventional calculationmethod of a motion vector between corresponding pixels between fields, areference field position is calculated by the same method describedbelow, regardless of whether the coding field or reference field is atop field or a bottom field. Specifically, a motion vector 211 (X,Y) andcoding field coordinates 212 (X_(s), Y_(s)) are inputted to a pixelcorresponding unit 210, and as reference field coordinates 213,coordinates (X_(s)+X, Y_(s)+Y) is given.

The definition of the relation between a vector and a pixel positionapplies to both a luminance component and chrominance component. InMPEG-1/MPEG-2/AVC FCD, which all are general motion picture encodingmethods, only the vector of a luminance component is encoded, and thevector of a chrominance component is calculated by scaling down theluminance component. Particularly, in AVC FCD, since the number ofvertical pixels and that of horizontal pixels of a chrominance componentare a half of those of a luminance component, respectively, it isspecified that a motion vector used to calculate the predictive pixel ofa chrominance component should be obtained by accurately scaling downthe motion vector of the luminance component to a half.

FIG. 10 shows a conventional method for calculating a chrominance motionvector using a luminance motion vector.

Specifically, if a luminance motion vector 221 and a chrominance motionvector 222 are (MV_x, MV_y) and (MVC_x, MVC_y), respectively, achrominance motion vector generation unit 220 can calculate achrominance motion vector 222 according to the following equation.

(MVC_x,MVC_y)=(MV_x/2,MV_y/2)  (1)

This conventional calculation method can be used regardless of whether amotion vector is used for prediction between fields with the same parityor between fields with different parity.

In AVC FCD, as the accuracy of the motion vector of a luminancecomponent, ¼ pixel accuracy can be applied. Therefore, as a result ofequation (1), as the accuracy of the motion vector of a chrominancecomponent, a vector having ⅛ pixel accuracy, that is, accuracy at thedecimal fraction, can be used.

FIG. 11 shows the calculation method of the interpolated pixel of achrominance component that is defined in AVC FCD.

In FIG. 11, a black circle and a white circle represent an integer pixeland an interpolated pixel, respectively. In this case, the horizontalcoordinate of an interpolated pixel G(256) is obtained by internallydividing each horizontal coordinate between points A(250) and C(252) ata ratio α:1−α, and the vertical coordinate can be obtained by internallydividing each vertical coordinate between points A(250) and B(251) atβ:1−β. In this case, a and P are a value between 0 and 1. Aninterpolated pixel G(256) defined by such positions can be roughlycalculated as follows using integer pixels A(250), B(251), C(252) andD(253), which are located around the interpolated pixel G(256), andusing α and β.

G(1−α)·(1−β)·A+(1−α)·β·β+α(1−β)·C+α·β·D   (2)

The interpolated pixel calculation method of a chrominance component,using the method shown in FIG. 11 is just one example, and there is noproblem in using another calculation method.

In the case of this field encoding mode, in a prediction in which anoriginal image field and a reference field are different, that is,between fields with different parity, the respective zero vectors of themotion vector of a luminance component and that of a chrominancecomponent are not parallel in the definition of AVC FCD. Specifically,if a prediction is made using the motion vector of a chrominancecomponent calculated using the motion vector of a luminance componentaccording to the conventional definition, a pixel located in a positionspatially deviated from that of the luminance component is to bereferenced. This fact is described below with reference to FIG. 12. InFIG. 12, it is assumed that a top field 130, a bottom field 131 and atop field 132 continue timewise. In this case, bottom field 131 is to beencoded using top field 130. In this inter-field encoding, the verticalmotion vector in the same line of each field is defined to be zero.Therefore, if a zero vector (0, 0) is assigned to a luminance pixel 133a that belongs to the second line of bottom field 131, this pixel can bepredicted from a pixel 135 a in top field 130. Similarly, when a zerovector (0, 0) is assigned to a chrominance pixel 133 a which belongs tothe first line of the bottom field 131, this pixel is predicted from thepixel 137 a which is in the first line of chrominance of the top field130. Similarly, a luminance pixel 133 b in the third line and achrominance pixel 134 b, which belong to top field 132 are predictedfrom pixels 135 b in the third line of luminance and 137 b in the secondline of chrominance in bottom field 131, respectively. Since essentiallyit is preferable that a chrominance motion vector and a luminance motionvector are parallel, chrominance pixels 134 a and 134 b should bepredicted from the positions 136 a and 136 b, respectively, if aluminance motion vector is as it is.

As described earlier, in a prediction between fields with differentparity, the fact that the respective zero vectors of luminance andchrominance are not parallel is explained. In the case of AVC FCD, thisfact causes the following problems for all vectors in a predictionbetween fields with different parity. FIGS. 13 and 14 show suchproblems. Problems in the case of AVC FCD are described below. In theexplanation below, a horizontal component of a motion vector is set tozero in all cases for brevity.

FIG. 13 shows a conventional problem caused if a chrominance motionvector is conventionally calculated using a luminance motion vector whena reference field and a coding field are a bottom field and a top field,respectively. In AVC FCD, since, as is clear from equation (1), it isspecified that the number of vertical and horizontal pixels of achrominance component are a half of those of a luminance component, amotion vector used to calculate the predictive pixel of a chrominanceshould be scaled down to a half of the motion vector of a luminancecomponent. This is regardless of whether a motion vector is used forprediction between frames, between fields with the same parity orbetween fields with different parity.

It is shown below that this definition causes a problem when achrominance motion vector is calculated using a luminance motion vectordefined between fields with different parity. In FIG. 13, a coding fieldtop field luminance pixel 140 in the first line has (0,1) as apredictive vector, and as a result, it points a bottom reference fieldluminance pixel position 141 in the second line as a predictive value.

In this case, a chrominance motion vector that belongs to the same blockis calculated to be (0, ½), according to equation (1). If a predictionis made using motion vector (0, ½) as a predictive value of a codingfield top field chrominance-pixel 142 in the first line, a pixelposition 143 is used as predicted value, which shifts downward by half apixel from a pixel in the first line of a bottom reference fieldchrominance component.

In this case, a luminance motion vector (0,1) and a chrominance vector(0,½) are not parallel. It is preferable to use a bottom reference fieldchrominance predictive pixel position 145 to which a chrominance motionvector parallel to a luminance motion vector is applied.

FIG. 14 shows a conventional problem caused if a chrominance motionvector is calculated using a luminance motion vector when a referencefield and a coding field are a top field and a bottom field,respectively. As described in FIG. 13, in FIG. 14, a bottom coding fieldluminance pixel 150 in the first line has (0,1) as a predictive vector,and as a result, it points a reference top field luminance pixelposition 151 in the second line as a predictive value.

In this case, a chrominance motion vector that belongs to the same blockis calculated to be (0,½), according to equation (1). If a prediction ismade using motion vector (0, ½) as a predictive value of a bottom codingfield chrominance pixel 152, a pixel position 153 is used as predictedvalue which is shifted by half a pixel from a top reference fieldchrominance pixel position 153 in the first line.

In this case, a luminance motion vector (0,1) and a chrominance vector(0, ½) are not parallel. It is preferable to use a top reference fieldchrominance predictive pixel position 155 to which a chrominance motionvector parallel to a luminance motion vector is applied.

As described above, if a reference field parity and a coding fieldparity are different, according to the conventional predictive method, apixel located in the position of a luminance component spatiallydeviated from that of the chrominance component is to be referenced, anda predictive image, in which a pixel located in the position of aluminance component is spatially deviated from that of the chrominancecomponent, is generated not only for a zero vector but for all thevectors. Note that, in the above explanation, vector are said to beparallel or not parallel by considering the case where the direction intime of a luminance motion vector and a chrominance motion vector, thatis, time direction from coding field to reference field in included in amotion vector. The same is true below.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a motion pictureencoding device and a motion picture decoding device capable ofparticularly improving predictive efficiency of a chrominance componentand improving encoding efficiency accordingly, in encoding betweendifferent field images.

The motion picture encoding device of the present invention for makingthe inter-field motion compensation of a motion picture signal composedof a plurality of fields comprises a plurality of chrominance motionvector generation units generating a chrominance motion vector using aluminance motion vector in a motion picture encoding device; and aselection unit selecting one of the chrominance motion vector generationunits used to generate a chrominance vector, using the reference fieldparity and coding field parity of a motion vector. The chrominancemotion vector generation unit selected by the selection unit generatesthe chrominance predictive vector, based on the motion vectorinformation of luminance information.

The motion picture decoding device of the present invention for makingthe inter-field motion compensation of a motion picture signal composedof a plurality of fields comprises a plurality of chrominance motionvector generation units generating a chrominance motion vector from aluminance motion vector; and a selection unit selecting one of thechrominance motion vector generation units used to generate achrominance vector, using the reference field parity and coding fieldparity of a motion vector. The chrominance motion vector generation unitselected by the selection unit generates the chrominance predictivevector, based on the motion vector information of luminance information.

According to the present invention, since a chrominance motion vectorwhich is generated by a suitable method based on parities of aencoding/decoding field and a reference field, is used, the discrepancyof the chrominance motion vector caused by the difference ofarrangement, or the way of assignment to a top and a bottom field ofluminance pixels and chrominance pixels, is resolved.

Additionally, by the present invention, a chrominance motion vectorwhich is parallel to a luminance motion vector is obtained even in thecase of fields with different parity, and the problem of a shift ofreference pixel position between luminance components and chrominancecomponents in the conventional method, is resolved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an inter-frame predictive encodingdevice;

FIG. 2 shows the respective positions of luminance and chrominancepixels and a field to which each of them belongs;

FIG. 3 shows the respective vertical time and spatial positions ofluminance and chrominance pixels in a field image;

FIG. 4 shows the relation between a field and a frame in a frameencoding mode;

FIG. 5 shows a predictive method in an inter-frame predictive encodingmode;

FIG. 6 shows a predictive method in an inter-field predictive mode;

FIG. 7 shows the coordinates of a field image;

FIG. 8 shows the conventional calculation method of a motion vectorbetween corresponding pixels between fields;

FIG. 9 shows the conventional calculation method of a pixel pointed by amotion vector;

FIG. 10 shows a conventional method for calculating a chrominance motionvector, using a luminance motion vector;

FIG. 11 shows the calculation method of an interpolated pixel of achrominance component;

FIG. 12 shows the principle of conventional direct mode for explaining azero vector between fields with different parity;

FIG. 13 shows a conventional problem caused if a chrominance motionvector is calculated using a luminance motion vector when a referencefield and a coding field are a bottom field and a top field,respectively;

FIG. 14 shows a conventional problem caused if a chrominance motionvector is calculated using a luminance motion vector when a referencefield and a coding field are a top field and a bottom field,respectively;

FIG. 15 shows the method for generating a chrominance motion vector,using a luminance motion vector in the present invention;

FIG. 16 shows the operation of one preferred embodiment of the firstchrominance motion vector generation unit of the present invention;

FIG. 17 shows the operation of one preferred embodiment of the secondchrominance motion vector generation unit of the present invention;

FIG. 18 is the operation of one preferred embodiment of the thirdchrominance motion vector generation unit of the present invention;

FIG. 19 is the operation of one preferred embodiment of the selectionunit of the present invention;

FIG. 20 is one example of the present invention which calculates achrominance motion vector using a luminance motion vector when areference field and a coding field are bottom and top fields,respectively; and

FIG. 21 is one example of the present invention which calculates achrominance motion vector using a luminance motion vector when areference field and a coding field are top and bottom fields,respectively.

FIG. 22 shows the operation of another preferred embodiment of the firstchrominance motion vector generation unit of the present invention;

FIG. 23 shows the operation of another preferred embodiment of thesecond chrominance motion vector generation unit of the presentinvention;

FIG. 24 is the operation of another preferred embodiment of the thirdchrominance motion vector generation unit of the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, the principle of coding in the present invention is described.

The motion picture encoding device of the present invention for makingthe inter-field motion compensation of a motion picture signal composedof a plurality of fields comprises a plurality of chrominance motionvector generation units generating a chrominance motion vector using aluminance motion vector; and a selection unit selecting one of thechrominance motion vector generation units used to generate achrominance vector, using the respective parity of the reference fieldand a coding field of a motion vector. The chrominance motion vectorgeneration unit selected by the selection unit generates the chrominancepredictive vector, based on the motion vector information of luminanceinformation.

If a chrominance motion vector from a coding field to a reference fieldis parallel to a luminance motion vector from the coding field to thereference field, the spatial shift of the luminance motion vector andthat of the chrominance motion vector become the same, that is, therelation of the spatial positions of the luminance motion vector and thechrominance motion vector is preserved, then the color displacementbetween fields disappears.

Here, the important thing is that, in conventional method, even if theluminance motion vector is parallel to the chrominance motion vectorbased on a mathematical expression, each does not become parallel whenthose vectors are mapped on relations between luminance pixels andbetween chrominance pixels which compose each field.

The plurality of chrominance motion vector generation units include thethree following types.

A first chrominance motion vector generation unit is selected by theselection unit when a reference field and a coding field have the sameparity. A second chrominance motion vector generation unit is selectedby the selection unit when a reference field and a coding field are atop field and a bottom field, respectively. A third chrominance motionvector generation unit is selected by the selection unit when areference field and a coding field are a bottom field and a top field,respectively.

A method for calculating a chrominance motion vector parallel to aluminance motion vector depends on the coding field parity and referencefield parity of a luminance motion vector. The calculation methoddiffers in the following three case: a case where the coding fieldparity and reference field parity are the same, a case where the codingfield and reference field are top and bottom fields, respectively, and acase where the coding field and reference field are bottom and topfields, respectively. Therefore, in the present invention, an optimalone is selected from the three types of chrominance motion vectorgeneration units calculating a chrominance motion vector parallel to aluminance motion vector, depending on the coding field and the referencefield, and a chrominance motion vector is generated.

Specifically, if the reference field parity and coding field parity arethe same, the first chrominance motion vector generation unit calculatesa chrominance motion vector as follows, assuming that a luminance motionvector indicating the vertical displacement of one luminance pixel of afield image by the value “1” of the vector component as units and achrominance motion vector indicating the vertical displacement of onechrominance pixel of a field image by the value “1” of the vectorcomponent as units are MVy and MVCy, respectively.

MVCy−Mvy/2  (3)

If the reference field parity and coding field parity are top and bottomfields, respectively, the second chrominance motion vector generationunit calculates a chrominance motion vector as follows, assuming that aluminance motion vector indicating the vertical displacement of oneluminance pixel of a field image by the value “1” of the vectorcomponent as units and a chrominance motion vector indicating thevertical displacement of one chrominance pixel of a field image by thevalue “1” of the vector component as units are MVy and MVCy,respectively.

MVCy−Mvy/2+0.25  (4)

If the reference field parity and coding field parity are bottom and topfields, respectively, the third chrominance motion vector generationunit calculates a chrominance motion vector as follows, assuming that aluminance motion vector indicating the vertical displacement of oneluminance pixel of a field image by the value “1” of the vectorcomponent as units and a chrominance motion vector indicating thevertical displacement of one chrominance pixel of a field image by thevalue “1” of the vector component as units are MVy and MVCy,respectively.

MVCy=Mvy/2−0.25  (5)

Sometimes, the respective units of luminance and chrominance vectorsvary, depending on its definition. In the case that it is defined that aluminance motion vector indicates the displacement of one luminancemoving pixel when the component of the luminance motion vector changesby value 4 and that a chrominance motion vector indicates thedisplacement of one chrominance moving pixel when the component of thechrominance motion vector changes by value 8, if the reference fieldparity and coding field parity are the same, the first chrominancemotion vector generation unit calculates a chrominance motion vector asfollows, assuming that a luminance motion vector and a chrominancemotion vector are MVy and MVCy, respectively.

MVCy=Mvy  (6)

In the same definition, if the parity of reference field and codingfield are top and bottom fields, respectively, the second chrominancemotion vector generation unit calculates a chrominance motion vector asfollows, assuming that a luminance motion vector and a chrominancemotion vector are MVy and MVCy, respectively.

MVCy=Mvy+2  (7)

In the same definition, if the reference field parity and coding fieldparity are bottom and top fields, respectively, the third chrominancemotion vector generation unit calculates a chrominance motion vector asfollows, assuming that a luminance motion vector and a chrominancemotion vector are MVy and MVCy, respectively.

MVCy=Mvy−2  (8)

The motion picture decoding device of the present invention basicallyhas the same functions as the motion picture encoding device, andoperates in the same way.

The preferred embodiments of the encoding device are mainly describedbelow. The encoding device has the configuration described above. Sincethe present invention relates to the vertical component of a motionvector, it is assumed for convenience sake that the horizontalcomponents of all the motion vectors are 0. In this case, the decodingdevice has the same configuration as the encoding device.

Preferred embodiments are described below assuming that AVC FCD isadopted.

FIG. 15 shows a method for calculating a chrominance motion vector usinga luminance motion vector. The preferred embodiment of a devicegenerating a chrominance motion vector using a luminance motion vectorin a field prediction comprises three types of chrominance motion vectorgeneration units and one selection unit.

The operation of the present invention shown in FIG. 15 is describedbelow. Firstly it is assumed that a given luminance motion vector 231 is(MV_x,MV_y). This luminance vector is inputted to all of a firstchrominance motion vector generation unit 233, a second chrominancemotion vector generation unit 234 and a third chrominance motion vectorgeneration unit 235. Then, their respective outputs are inputted to aselection unit 230. The selection unit 230 selects one of the respectiveoutputs of the first, second and third chrominance motion vectorgeneration units, based on information about the coding field parity 237of the inputted motion vector and its reference field parity 238, andoutputs it as a color motion vector 232 (MVC_x,MVC_y).

FIG. 16 shows the operation of the first chrominance motion vectorgeneration unit. In this preferred embodiment, a luminance motion vector261 (MV_x,MV_y) is inputted to a first chrominance motion vectorgeneration unit 260, and a first chrominance motion vector candidate 262(MVC1_x, MVC1_y) is outputted. The chrominance motion vector generationunit 260 calculates the first chrominance motion vector candidate 262 asfollows using the luminance motion vector 261.

(MVC1_x,MVC1_y)−(MV_x/2,MV_y/2)  (9)

Then, the calculated first chrominance motion vector candidate 262 isoutputted to the selection unit.

FIG. 17 shows the operation of the second chrominance motion vectorgeneration unit. In this preferred embodiment, a luminance motion vector271 (MV_x,MV_y) is inputted to a second chrominance motion vectorgeneration unit 270, and a second chrominance motion vector candidate272 (MVC2_x, MVC2_y) is outputted. The chrominance motion vectorgeneration unit 270 calculates the second chrominance motion vectorcandidate 272 as follows using the luminance motion vector 271.

(MVC2_x,MVC2_y)−(MV_x/2,MV_y/2+1/4)  (10)

Then, the calculated second chrominance motion vector candidate 272 isoutputted to the selection unit.

FIG. 18 shows the operation of the third chrominance motion vectorgeneration unit. In this preferred embodiment, a luminance motion vector281 (MV_x,MV_y) is inputted to a third chrominance motion vectorgeneration unit 280, and a third chrominance motion vector candidate 282(MVC2_x, MVC2_y) is outputted. The chrominance motion vector generationunit 280 calculates the third chrominance motion vector candidate 282 asfollows using the luminance motion vector 281.

(MVC3_x,MVC3_y)−(MV_x/2,MV_y/2−1/4)  (11)

Then, the calculated third chrominance motion vector candidate 282 isoutputted to the selection unit.

FIG. 19 shows the operation of one preferred embodiment of the selectionunit 240 of the present invention. Firstly, in this preferredembodiment, a condition judgment table 241 is used for judgment of thecoding field parity 247 of a motion vector and its reference fieldparity 248, and the selection information 249 of a chrominance motionvector generation unit to be selected is outputted. In this preferredembodiment, if the reference field and coding field are the same, thiscondition judgment table 241 is used for outputting selectioninformation indicating the selection of a first chrominance motionvector candidate 244. If reference field and coding field are top andbottom fields, respectively, the condition judgment table 241 is usedfor outputting selection information indicating the selection of asecond chrominance motion vector candidate 245. If reference field andcoding field are bottom and top fields, respectively, the conditionjudgment table 241 is used for outputting selection informationindicating the selection of a third chrominance motion vector 246candidate.

In this case, the first, second or third chrominance motion vectorcandidates 244, 245 and 246 are connected to 262 shown in FIG. 16, 272shown in FIG. 17 and 282 shown in FIG. 18, respectively. Then, aselector 243 selects one of the first, second and third chrominancemotion vector candidates 244, 245 and 246, based on the selectioninformation 249, and outputs (MVC_x,MVC_y) as its chrominance motionvector 242.

FIG. 20 shows the operation of the present invention to calculate achrominance vector using a luminance vector in the case where referencefield and coding field are bottom and top fields, respectively. In theexample shown in FIG. 20, a luminance motion vector (MV_x,MV_y) used topredict a top coding field pixel 160 is assumed to be (0,1). In thiscase, a reference field bottom field luminance pixel position 161 isselected for the prediction of a luminance pixel 160. The calculationprocess of a chrominance motion vector to be used to predict a topcoding field chrominance pixel 162 is described below with reference toFIG. 15.

Firstly, in FIG. 20, reference field and coding field are bottom and topfields, respectively. In this case, the condition judgment table 241shown in FIG. 19 is used for selecting selection information 249 aboutthe third chrominance motion vector candidate. According to equation(11), the third chrominance motion vector candidate is calculated asfollows.

$\begin{matrix}\begin{matrix}{( {{{MVC}\; 3{\_ x}},{{MVC}\; 3{\_ y}}} ) = ( {{{MV\_ x}/2},{{{MV\_ y}/2} - {1/4}}} )} \\{= ( {{0/2},{{1/2} - {1/4}}} )} \\{= ( {0,{1/4}} )}\end{matrix} & (12)\end{matrix}$

Then, this value is outputted as the chrominance motion vector 242 shownin FIG. 19. If this vector (0,¼) is applied to the top coding fieldchrominance pixel 162, a bottom reference field chrominance pixelposition 163 is used as a predicted value. In FIG. 20, the verticalpositional relation between pixels corresponds to a real pixel. As isclear from FIG. 20, a luminance motion vector (0,1) and a chrominancemotion vector (0, ¼) are parallel. Thus, the color deviation betweenluminance and chrominance components, which is a conventional problem,can be solved by the present invention.

Similarly, FIG. 21 shows the operation of the present invention tocalculate a chrominance vector using a luminance vector in the casewhere reference field and coding field are top and bottom fields,respectively.

In the example shown in FIG. 21, a luminance motion vector (MV_x,MV_y)used to predict a bottom coding field pixel 170 is assumed to be (0,1).In this case, a top reference field luminance pixel position 171 isselected for the prediction of a luminance pixel 170. The calculationprocess of a chrominance motion vector to be used to predict a bottomcoding field chrominance pixel 172 is described below with reference toFIG. 15.

Firstly, in FIG. 21, reference field and coding field are top and bottomfields, respectively. In this case, the condition judgment table 241shown in FIG. 19 is used for selecting selection information 249 aboutthe second chrominance motion vector candidate. According to equation(10), the candidate second chrominance motion vector is calculated asfollows.

$\begin{matrix}\begin{matrix}{( {{{MVC}\; 2{\_ x}},{{MVC}\; 2{\_ y}}} ) = ( {{{MV\_ x}/2},{{{MV\_ y}/2} + {1/4}}} )} \\{= ( {{0/2},{{1/2} + {1/4}}} )} \\{= ( {0,{3/4}} )}\end{matrix} & (13)\end{matrix}$

Then, this value is outputted as the chrominance motion vector 242 shownin FIG. 19. If this vector (0,¾) is applied to the bottom coding fieldchrominance pixel 172, a top reference field chrominance pixel position173 is used as a predictive position. In FIG. 21, the verticalpositional relation between pixels corresponds to a real one. As isclear from FIG. 21, a luminance motion vector (0,1) and a chrominancemotion vector (0, ¾) are parallel. Thus, the color deviation betweenluminance and chrominance components, which is a conventional problem,can be solved by the present invention.

Although in the examples shown in FIGS. 20 and 21, the prediction of aspecific vector is described, in a prediction between other parityfields, a prediction in which there is no deviation between luminanceand chrominance can also realized by applying this preferred embodiment.

When the reference field parity and coding field parity are the same,such color deviation does not occur. Therefore, the result of the firstchrominance motion vector generation unit 233 of the present inventionwhich has the same configuration as a chrominance motion vectorgeneration unit 220 is selected from the conventional luminance motionvector shown in FIG. 10, and is used as a color motion vector 232. Sincein this case, a chrominance motion vector calculated by the presentinvention is the same as conventional one, the description of thispreferred embodiment is omitted here.

In another aspect of the present invention, equations (9), (10) and (11)vary depending on the units of luminance and chrominance motion vectors.

FIGS. 22 through 24 show another embodiment of the first chrominancemotion vector generation unit, the second chrominance motion vectorgeneration unit and the third chrominance motion vector generation unitof the present invention.

In the case that it is defined that a luminance motion vector indicatesthe displacement of one luminance moving pixel when the value of theluminance motion vector changes by four and that a chrominance motionvector indicates the displacement of one chrominance moving pixel whenthe value of the chrominance motion vector changes by eight, achrominance motion vector generation unit 260 a calculates a candidatefirst chrominance motion vector 262 a using a luminance motion vector261 a as follows.

(MVC1_x,MVC1_y)−(MV_x,MV_y)  (14)

Then, the calculated first chrominance motion vector candidate 262 a isoutputted to a selection unit.

The chrominance motion vector generation unit 270 a calculates a secondchrominance motion vector candidate 272 a using a luminance motionvector 271 a as follows.

(MVC2_x,MVC2_y)−(MV_x,MV_y+2)  (15)

Then, the calculated second chrominance motion vector candidate 272 a isoutputted to a selection unit.

The chrominance motion vector generation unit 280 a calculates a thirdchrominance motion vector candidate 282 a using a luminance motionvector 281 a as follows.

(MVC3_x,MVC3_y)−(MV_x,MV_y−2)  (16)

Then, the calculated third chrominance motion vector candidate 282 a isoutputted to a selection unit.

Although this preferred embodiment is described assuming that it adoptsAVC FCD, this is just one preferred embodiment, and the format forencoding a field image is not limited to this.

According to the present invention, a chrominance motion vector parallelto a luminance motion vector can also be calculated in fields withdifferent parity, and the deviation in a reference pixel positionbetween luminance and chrominance components, which are the conventionalproblem, can be solved accordingly.

1. A motion picture encoding device for making an inter-field motioncompensation prediction and for executing an encoding process on amotion picture signal, wherein each frame has two fields and a number ofpixels of a chrominance vertical component is different than a number ofpixels of a luminance vertical component, the motion picture encodingdevice comprising: an encoder configured to generate a chrominancemotion vector from a luminance motion vector based on an equationrepresented asMVCy=MVy/2+0.25 when a reference field is a top field and a coding fieldis a bottom field, so that the generated chrominance motion vector andthe luminance motion vector are thereby parallel, wherein MVy representsthe luminance motion vector which indicates a vertical directionmovement of a luminance pixel of a field image and MVCy represents thechrominance motion vector which indicates a vertical direction movementof a chrominance pixel of the field image.
 2. The motion pictureencoding device according to claim 11, wherein the chrominance motionvector is generated from the luminance motion vector based on anequation represented asMVCy=MVy/2 when both the reference and coding fields are top fields orare bottom fields.
 3. The motion picture encoding device according toclaim 2, wherein: the encoder adaptively selects a method which uses oneof the calculations to generate the chrominance motion vector from theluminance motion vector which depends on parities of the reference fieldand the coding field.
 4. A motion picture encoding device for making aninter-field motion compensation prediction and for executing an encodingprocess on a motion picture signal, wherein each frame has two fieldsand a number of pixels of a chrominance vertical component is differentthan a number of pixels of a luminance vertical component, the motionpicture encoding device comprising: an encoder configured to generate achrominance motion vector from a luminance motion vector based on anequation represented asMVCy=MVy/2−0.25 when a reference field is a bottom field and a codingfield is a top field so that the generated chrominance motion vector andthe luminance motion vector are thereby parallel, wherein MVy representsthe luminance motion vector which indicates a vertical directionmovement of a luminance pixel of a field image, and MVCy represents thechrominance motion vector which indicates a vertical direction movementof a chrominance pixel of the field image.
 5. The motion pictureencoding device according to claim 4 wherein the chrominance motionvector is generated from the luminance motion vector based on anequation represented asMVCy=MVy/2 when both the reference and coding fields are top fields orare bottom fields.
 6. The motion picture encoding device according toclaim 5, wherein the encoder adaptively selects a method which uses oneof the calculations to generate the chrominance motion vector from theluminance motion vector which depends on parities of the reference fieldand the coding field.
 7. A motion picture encoding device for making aninter-field motion compensation prediction and for executing an encodingprocess on a motion picture signal, wherein each frame has two fieldsand a number of pixels of a chrominance vertical component is differentthan a number of pixels of a luminance vertical component, the motionpicture encoding device comprising: an encoder configured to determinewhether each of a reference field and a coding field is a top field or abottom field, and configured to generate a chrominance motion vectorfrom a luminance motion vector based on a first calculation when boththe reference and coding fields are top fields or are bottom fields,based on a second calculation when the reference field is a top fieldand the coding field is a bottom field, and based on a third calculationwhen the reference field is a bottom field and the coding field is a topfield.
 8. The motion picture encoding device according to claim 7wherein the first calculation is represented as MVCy=MVy/2, the secondcalculation is represented as MVCy=Mvy/2+0.25 and the third calculationis represented as MVCy=MVy/2−0.25 wherein MVy represents the luminancemotion vector which indicates a vertical direction movement of aluminance pixel of a field image, and MVCy represents the chrominancemotion vector which indicates a vertical direction movement of achrominance pixel of the field image.
 9. A motion picture encodingdevice for making an inter-field motion compensation prediction and forexecuting an encoding process on a motion picture signal, wherein eachframe has two fields and a number of pixels of a chrominance verticalcomponent is different than a number of pixels of a luminance verticalcomponent, the motion picture encoding device comprising: means fordetermining whether each of a reference field and a coding field is atop field or a bottom field, and means for generating a chrominancemotion vector from a luminance motion vector based on a firstcalculation when both the reference and coding fields are top fields orare bottom fields, based on a second calculation when the referencefield is a top field and the coding field is a bottom field, and basedon a third calculation when the reference field is a bottom field andthe coding field is a top field.
 10. The motion picture encoding deviceaccording to claim 9 wherein the first calculation is represented asMVCy=MVy/2, the second calculation is represented as MVCy=Mvy/2+0.25 andthe third calculation is represented as MVCy=MVy/2−0.25 wherein MVyrepresents the luminance motion vector which indicates a verticaldirection movement of a luminance pixel of a field image, and MVCyrepresents the chrominance motion vector which indicates a verticaldirection movement of a chrominance pixel of the field image.